18: 11639 ( Part 1 ) .. 1986
(Reaffirmed 2001 )

flu/ian Standard
CRITERIA FOR STRUcrURt\L DESIGN OF PENSTOCKS
PART 1 SURFACE PENSTOCKS

INDIAN STANDARDS INSTITUTION
M,~~.t\K

£JIJ\V ~".

9

1l,r\lI~\l)CK

NF.'V
Gr4

nm.m

SJ1,\11 1100(;2

4.*\f.\R

1\L\1tO

AMENDMENT NO. 1 DECEMBER 2008 TO IS 11639 (PART 1) : 1986 CRITERIA FOR STRUCTURAL DESIGN OF PENSTOCKS

[Page 9, clause 6.1.5.1(b)] Substitute ` f 3 =

µ1 PAc
A

' for ` f 3 = µ1 PAc '.
2

(Page 11, clause 7.1) Substitute ` Sx, Sy =

fx + fy fx - fy ± + q2 2 2

' for ` Sx, Sy =

fx + fy ± 2

( fx - fy ) 2 + q 2 '.
2

(WRD 14)
Reprography Unit, BIS, New Delhi, India

IS I 11639( Part 1) · 1916

Indian Standard
CRITERIA FOR STRUCTURAL DESIGN OF PENSTOCKS
PART 1 SURFACE PENSTOCKS Water Conductor Systems Sectional Committee, BDC 58
Chairrrwl .
SlIal P. M. MAN. 39 Sbivaji Co-operative Housing Society Pune

M""b",

R,prI"rding

08181' ENODf&JIlR Bhakra Beal Management Board, Chandigarb SKl\I SUDIlR8BAN KUMAR (AICIl'll4l, ) C:smr ENOnnDn Mukerian Hydel Project Design, Chandigarh DIBBCTOR (Alt"nal.) C B I 11., ENG I N 11 11 B (CIVIL Karnataka Power Corporation Limited, Bangalore DJDSIGNS)
SURI P. R. MALLmABJU:NA (Altlt1UJl,) CalEr ENGINB.a ( GB1UmA.L ) Public Works Department, Madras CRlllr EXGm_ ( IRRIGATION) ( .Alt"n." ) CHIB" ENGm.a (HP) Tamil Nadu Electricity Board, Coimbatore SUPJIlRIN'1'1INDDfG ElfonfJum ( AIUr".t, ) CBIBI' ENGINBBB (IRBIOATIOK Public Works and Electricity Department, Mysore SOUTH) SUPBRllftElmJXO EMGJ1C'DB. ( Alt",.at, ) SIIBI C. ETTY DA.BWIN In personal capacity (Dunery Mutlada P.O.,

DIREOTOR

TrivtJntlrum) Central Soils aDd Materials Research Station, New Delhi
AlllrfUll, )

D..UTY DIRIICTOB ( DIRZCTOR (HeD-I) DEPUTY DIRECTOB ( DB A. K. DUBS

Central Water Commission, New Delhi HCD-I ) (Alt"".") Central Minin, Research Station Unit, Roorkee D1\ J. L. jmTHwA (AlI",",t,) Smu j. P. GUPTA Power House DesigDl, Irrigation Department, Roorkee SR.l A. P. GtrPT A ( Alumau ) SKBJ M. V. S. IYENOAR Hinduatan Construction Co Ltd, New Delhi SHRI M. G. KHAN (AlterM")

( C",,';nUld 011/Jag' 2 )

I

C>C~"'1986

INDIAN STANDARDS INSTITt1rION This publication is protected under tIM lrulia CoJ!1rilAt Ad (XIV of 1957) aDd reprodue:tloo la whol. or In part by aDy meaDi except with written penniulon or the pub"· · IhaII be deemed to be aD IDlrlapm_t of copyright under the laid Act.

II · 11631 ( .... t 1 ) .. 1. .
( Con'inuld .from /HII' 1 )
Mmajn.l
JOJN'1'

D'.BlIlOTOB,

RUB"RCU

(GE·I1 )
SURt SHRt

P. N. KIIAB

A. K.

M:&STA

Kerala State Electricity Board, Trivaadrum Water Resources Development Trainiq Centre, Roork.. SIlBI G. P AKT Geololical Survey of Iadia, New D.lhi SHRI N. K. MANDWAL ( AllmuJl,) SHIU A. R. RAIOHU. In personal capacity ( 147, Gartd;',..,ar, BomN.1 ) SUllI Y. RAilA KRISHNA RAO Andbra Pradesh State Electricity Board, Hyd4Prabad
S'O!'llBl1ftmfDINO EIfGDfJDlt ( DUIOK AND PLAN1(ING ) ( Altma4U ) REFR.SUTATIVJD .. Central Water and Power Research Station, SHBI A. V. GOPALAJcBJ8BNA (AII6f'1UJu) SURI G. V. SATHAY1II General De.ilftS Or,uization, N..ik 88RI S. C. SilK Allam State Electricity Board, Guwahati SBBIN.K.DA8(~hnuu) Central Electricity Authority, New Delhi DB H. R. SUARMA Himachal Prad.b State Electricity SSRI A. K. SaIXANTIAB

BALI ( MBKBER ( CIVIL) DR B. PAn

SUI S. C.

Reaearch Desi._ and Standard. OrranizatioD, Lucknow National Hydroelectric Power Corporation Ltd, New Delhi Nadonal Projects Construction Corporation Limited, New Delbi

R''''''IfI'in,

AI,,,,",,,)

Pune

*

Board,

SHaI RutJODH SINGH SURI G. RAMAN,

Sundemapr (AlI"na") Director General, lSI (&-of/ido Mllllh,,)

Director ( Civ En" )

S",,'ary
SHar HBKANT KtrKAR

Deputy Director ( Civ Enn ). lSI

Panel for Penstocks and Anchor Blocks, BDC 58: P6
National Hydroelectric Power CorporatioD Limited, New Delhi Mnnhn, SURI M. L. AQ()A aw AL Bhakra Deal MaD.gement Board. Chandigarb SSKI Y. P. NAYAR (All,mat,) DIRECTOR (T & P) Irrisation Work&, GovemmeDt of PuDjab. Chandigarh SmnoR Da10N EWOINlIlER ( Altmlat. ) DtRlIlCTOB (HOD·} ) Central Water Commission, New Delhi DEPUTY DIRECTOR ( HOn.! ) ( AltmalJ") SJl1\l N. C. J,UN Irrigation Department, Government of Uttar Pradesh Lucknow DR ZAWAR MaBDI Bharat Heavy Electric." Ltd, Bhopal SSRI j. L. KBoal: ( Altmaat, ) ( CMlillIIId", /141' IS)

C"IIHn',. KUKAJU E. D1VATIA

.Chairman for the meetins.

2

II, 11631 ( ··"t 1 ) · 1986

Indian Standard
CRITERIA FOR

STRUCTURAL DESIGN OF PENSTOCKS
PART 1 SURFACE PENSTOCKS

o.

FOR EWOR D

0.1 This Indian Standard (Part 1) was adopted by the Indian Standards Institution on 31 January 1986, after the draft finalized by the Water Conductor Systems Sectional Committee had been approved by the Civil Engineering Division Council.
0.2 Conduits carrying water from surge tanks or directly from a reservoir, fore bay , to the power house are known as penstocks. Penstocks are generally of concrete or steel or a combination of both. The pressure varies from minimum at the upstream end to the maximum at the junction with the scroll case.

1. SCOPE

1.1 This standard ( Part 1 ) lays down the various forces acting on surface penstocks and structural design of penstocks conveying water under pressure flow cpnditions. However, this does not cover specials of pen.. stocks like penstock supports, manifolds, bends, expansion joints, manholes, branch outlets, etc.

2. NOTATIONS
2.1 For the purpose of this standard, the following notations shall have the meaning indicated against each: A = cross-sectional area of pipe shell material, mm! Ar = cross sectional area of stiffener ring, mm s b =- width of ring girder or stiffener ring, mm C == moment coefficient E - modulus of elasticity fl, fl, fa == longitudinal strelsel, N/mml If, = secondary bending Itress, N/mm l

IS I 11&31 ( Part 1 ) · 19.

fa I L M, Ml

total circumferential Itres., N/mml

f, - total longitudinal stresl, N/mml

= span length of pipe, mm
=
moments

= height of .tilFener ring or riDg girder, mm

P - internal pressure including water hammer, N/mml PI = total reaction at support, N

=- shear stress, N/mm2 , == radius of pipe shell, mm '1 - mean radius of shell, mm S =a hoop stress in pipe, N/mml S, .. equivalent stres., N/mml S., S. = principal stresses, N/mml T = temperature rise or drop, 00 I = thickness of pipe shell, mm '1 == thickness of stiffener ring or ring girder, rom W =- total distributed weight, that i., lelr-weight of shell weight of water, N/rn l . WI = total weight, that is, weight of shell weight of water, N Z os section modulus of pipe shell, rna ~ =s coefficient of linear expansion or contraction of pipe shell material, per 00 .",. =a coefficient of friction.
ql

+

+

3. DATA REQ,VIRED
3.1 The following data is required penstocks: for the structural design of

a) General drawing of installation; b) Complete longitudinal profile; c) Type of penstock; i) Free penstock pipe laid in a tunnel, and ii) Steel lined pressure shaft. d) Geological data; i) Geology of area. ii) Type of ground/rock, iii) Bearing capacity of ground,

4

· a 11&39 ( Part I ) · 19.
iv) Shear properties of soil, v) Modulul of deformation, and vi) Seismic coefficient. e) Climatic conditions; i) Temperature ( maximum, mean, minimum, by day and night and in summer and winter ), ii) Wind conditions ( direction and maximum speed ), and iii) Snow conditions ( period and average depth of snow). f ) Hydraulic data; i) Diameter of penstock, and ii) Discharge through penstock.

4. LOADS ON PBNSTOCK 4.1 The following are the main loads considered for the design of penstocks:
a) Internal water pressure, b) Weight of penstock and water, and c) Temperature. In addition, the other loads considered depend ing on location

are:
a) wind load,

b) snow load, and c) seismic forces. 4.2 The loads given in 4.1 are of the following nature: a) Permanent loads, b) Intermittent loads, and c) Exceptional load ·.

f.2.1 The loads of permanent nature are the forces which act upon the penstock in normal operation. They correspond to:
a) The maximum operating pressure which is the sum of maximum Itatic pressure and over pressure due to water hammer under

normal operating conditions, taking into account the oscillations in surge tank; b) The weight of penstock and water between the supports; c) Spacing and type of supports;

5

IS a 11639 ( ....t 1 ) · 1911 d) The difference between the temperature which may exist in the penstock in normal operation and the temperature exi.ting when coupling up the sections during erection; e) Friction at suppon,; and f) Temperature variation. 4.2.2 The loads of intermittent nature are the forces which though not excep tional, do not arise often. The two main cases are:

a) Penstock during filling, and b) Empty penstock under partial vacuum. The forces to be taken into account in each case correspond to: a) The weight of penstock and water between the supports, b) The type and spacing between supports, c) The temperature effect, and d) Friction at supports.
In addition to the forces enumerated in <a> to (d), intermittent loads may also occur due to wind or snow load and earthquakes. 4.2.3 are: a) b) c) The loads of exceptional nature that may act upon the penstocks

Shop or site test; Erection stresset; Bad operation of safety devices during filling such al non-operation of air valves which would create vacuum inside during empting operation of penstocks; d) Pressure rise caused due to unforeseen operation of regulating equipment of turbine/pump distribution: i) In case of impulse turbine. pressure rise due to needle slam on JOSI of oil pressure or mechanical failure; and ii) In case of reaction turbine, turbine gates may be closed instantaneously at any time by action of governor manual control of main relay valve or by the emergency solenoid device. e) Stresses developed due to resonance in penstock (A. rar as possible, the frequency of penstock pipe in any reach shall not match with the frequency of machine, frequency of vortex shedding in the draft tube, frequency of the system, etc, and resonance shall be avoided )j and f) Seismic forces. 6

IS I 1163. ( Part I ) · 1· ·

5. STRESSES IN PENSTOCK SHELL
5.1 The streases in the penstock shell of surface penstocks are subjected to circumferential and longitudinal Itrelsel. The Itreuel in pipe at the mid-span and at the lupports are as below: a) AI mid-J/Jdn: i) Hoop strelses developed due to internal pressure equal to sum of static pressure due to maximum water level in reservoir or surge tank plus the dynamic pressure due to water hammer al calculated for operating conditions, ii) Longitudinal stressel developed due to its own weight aDd weight of water by beam action, iii) Longitudinal streue. developed due to sliding friction over the supports, and iv) Longitudinal stresses developed due to expanaion or contraction of penltock shell due to variation of temperature.
b) AI supports:

i) Circumferential Itresses developed at the supports due to bending caused by internal pressure, ii) Longitudinal Itresses due to secondary bending moments caused by the restraintl imposed by ring girder or stiffener rings, iii) Longitudinal stresses developed at the supports due to beam action, and iv) Longitudinal stresses developed by forces enumerated in 4.1.

5.2 The stresses in penstock shell shall also be checked to withstand the
stresses developed due to intermittent and exceptional loading and for the following forces: a) Longitudinal stresses developed due to earthquake and wind, b) Circumferential stresses developed due to pressure rise called by non-operation a8 specified in 4.2.3 (d), c) Longitudinal stresses developed due to wind, and d) Stressel developed due to filling and draining of penstocks.

6. METHOD 01' CALCULA.TlON

or STRESSES IN PIPE SHELL

6.1 The streues for different force. shall be calculated .. given in 6.1.1 to 6.1.7.

7

.. r

11639 ( Part 1 ) .1986

6.1.1 Hoop Stress Du« to Int"."al p"uu" '.1.1.1 The hoop stress developed due to internal pressure i. given
by:
t NOTB - The internal pressure P is due to stacic head

S =- .!!-

+ dynamic head.

1.1.2 Longiludinal Joint Effiei,,,e} ( , ) 6.1.2.1 It Shall be taken as 1-0 for fully radiographed joint. 6.1.3 LOfI,;tudinal StrtSJtJ DUI to B,arn Action 6.1.3.1 The stress developed due to self-weight and weight of water pipe Ipanning over supports due to beam action .hall be calculated by the following formula:

f - T N /m l
where

M

AI - bending moment caused due to self-weight and weight
of water.
NO'1'JI - BeDdiq moment, M. at mid-span and at support shall be calculated for each ca.. eoDiideriDi the pipe a. a beam Ipaoninl continuoUily over intermediate supporta

6.1.3.2 The longitudinal stre,sea developed due to radial strain eaused by internal pressure may be taken equal to 0'303 times the hoop ten'ion. 1.1.3.1 The longitudinal atressel developed due to seismic forces in the pipe spanning over the support due to beam action is equivalent to seismic coefficient times stresses calculated in 6.1.3.1. These stresses should be added to stresses calculated in 6.1.3.1. 6.1.3.4 The longitudinal stresses developed due to wind or snow load acting on the pipe spanning over the support are calculated as given in 6.1.3.1, where bending moment, M, is caused due to wind load or snow load.

6.1.t Longi'~tlinal S"'SJ DIAl to Sliding Fritl;t)n 6.1.t.l The maximum longitudinal stress developing over all supports within a section between an expansion joint and the subsequent support .haJl be calculated by the formula: I'. IPf + aEP/ J2 = -Awhere Pf =- total sliding friction in section between an expansion joint and subsequent support = ,..W, Cos ~,

---r-'
8

IS I 11639 ( Part 1 ) · III'
a

= eccentricity of frictional force relative to centre line of
penstock,
= section modulus of pipe shen, and

Z

~ =

angle of section under consideration with the horizontal.

The coefficient of friction, "" between shell and support shaU be taken from Table 1.
TABS 1 DICTION COEFFICIENTS FOR DIPnRENT MATERIALS ( Claus, 6.1.4.1 )

SL No.

TVI'E OJ' SOI'I'ORT

i) Steel OD concrete ii) Steel on concrete with asphalt rootiDI paper in
hetwe~n

0"60
0'50

iii) Steel on steel ( rusty ) iv) Steel OD ItMI ( Irea~ed ) v) Steel on steel with two layers of service .heets in between vi) Rocker support vii) Roller support Yiii) Concrete on concrete

graphite 0'15 0'10 0'75

6.1.5 T emplraturl StrlSS
6.1.5.1 Longitudinal stresses caused due to expansion or contraction of pipe shell shall be calculated by the following formulae: a) Pipe shell without expansion joint fa = EccT b) Pipe shell with expansion joint fa = 1-'1, PAc, where 1-'1 = coefficient of friction between packing material and pipe shell. and Ac -=- contact area between penstock shell and packing material
in rnrn'[,

6.1.6 Circumfirent;al Bending Stress,s at SupjJorts
6.1.6.1 Circumferential stresses at supports due to bending caused
by internal pressure shall be calculated by the following formula:

M - C PI r
9

II · 1113. (Part 1 ) · 1986
The value of C for different angles of support is given in Fig. 1. The effective length or shell resisting the bending moment is equal to 4 times the radiu. of the shell.
0·10
I I I I I I I I I I " , I '"

0-08

0-08

.' .
,
-1"'l'iI~

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'.
j

I
~I

.....
~ 0-0'
\£.

u

I

u \:

Pw.~~Tt~o=fACT~N
""'lli

OF
j

,. RADIUS OF SHELL

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~ 0·02 u

MOMENT

M.CX~'

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IJ

J I
~

J
J

'I
J

- "" ....
20

"'" "...... ..... ~~ "-

I I I I IV
~

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'~~:'V ~ ~,....~~
~
~

· ~~j ~:,,- v
,~,_,: If
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......
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~AlU£S

- .....
80

V

60

100

120

Of 8 IN OEGRE ES

Fro. 1

VARIATION OP CIRCUMPBRBNTlAL MOMENT AROUND SHELL RBSTINO ON SADDLB SUPPORT

6.1.7 Longiludin41 B",ding StrlSI DUI to &sl,a;,. by Rin, Girders or Sti/fi"". Rill,s (JI IhI Supports

6.1.7.1 The secondary bending strea due to restrain shall be calculated by the formula:

It ==
tIrt

A,

1°82 ( A' -~ + 1-561 ttl "

x.!!t

NOTa - Thil stre.. is local and tbe efFect shall b. talkeD for a distance of Slf where f - 1°285 on either side of tb. supportiq riaa and pipe thickness shall be increased.

if required, in this zoneo

10

IS I 11639 ( Part 1 ) · 1118
7. EQ,UIV ALENT STRESSES
7.1 The circumferential and longitudinal stresses obtained as lpecified in 6.1.1 to 6.1.7, shall be combined to obtain equivalent strellel in accordance with Hencky Mises Theory, given by the formula:

s, = ttl Szl + 811 ±
5 , S.,
z

= fz ;

SX S" f., :l: 4~(~/s~--2-Ji~.,~)ir--+-r

where

Iz - longitudinal stress, !., hoop stress, and q = shear strel.
c=

The equivalent stresses may be readily obtained from Fig. 2. 8. LINER THICKNESS 8.1 The liner thickness of an exposed penstock shall withstand the equivalent stress as specified in 7_
8.2 Notwithstanding the thickness obtained as specified in 8.1 and regardless of pressure, a minimum thickness of liner shan be provided to resist the distortjon during fabrication and erection. A minimum thickness of D in em. 8.3 No corrosion allowance i. recommended. Instead, it is suggested to paint the inside and the outside surface of pipe with a paint conforming to the relevant Indian Standard. 9. WORKING STRESSES AND FA.CTOR OF SAPETY

~o50

em is recommended where D i. the diameter of shell

9.1 Normal Operatbal CODdidoa 9.1.1 It is recommended that under normal operating condition AI specified in 4.2.1, the working stresses with a factor of safety of 3 based on the minimum ultimate tensile strength shall be adopted for design but in no case the maximum stress.s obtained in 7.1 shall exceed 0'5 times the specified minimum yield strength of material. 9.2 latermltteat LoacU·· CODdltlo. 9.2.1 I t is recommended that under intermittent loading condition as specified in 4.2.2, the working stre··es with a factor of safety of 2-5 based on minimum ultimate tensile strength shall be adopted for designs but in no case the maximum lueues obtained in 7.1 shan exceed 2/3 the specified minimum yield strength of material.

11

18 · 11639 ( Part 1 ) · 1986

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TENSION. THOUSANDS

2 EQ.UIV ALENT STRESS DIAGRAM 9.3 Exceptio. COllciltloD 9.3.1 Under exceptional loading condition as specified in 4.2.3, it is recommended that the working stresses with a factor of safety 2'0 based on minimum ultimate strength shall be adopted for design but in no case the maximum stresses obtained in 7.1 shan exceed 0'8 times the specified minimum yield strength of material.
Flo.

12

IS a 1163' ( Part I ) · 1986
( Conl;nu,dfrom pag. 2 )
Mmabers R,prls,nt;", Kerala State Electricity Board, Trivandrum A. R. RAGHAVAN Tamil Nadu Electricity Board, Madras Snn r T. RAMASWAMY Indian Hume Pipe Co Ltd, Bombay 81)1\1 B. RAMA8WAMY (AII,rnat,) DR H. R. SUAHMA Central Electricity Authority, New Delhi SlUU B. TnoMA8 Central Water & Power Research Station, Pune SHRI R. VIJAYAN' In personal capacity ( ECONS-Engi",,,s & Corantltllllts, 35/136 KamalhHath LAn" eIKh", ) SURl N. G. KURUP ( Altlf"a/, )

SlUU SHRI

c. GENlt8A PILLAl

13

INTERNATIONAL SYSTEM 0. UNITS ( 81 UNITS)
···· VDlt.
Q;UAlftl'l'Y UNIT

SYIIBOL

LenKth Mau Time Electric current Thermodynamic temperature LuminoUi intenalty Amount of substance ...........tarJ Valt.

metre kllopam second ampere llelvin candela mole

m

kl
A

K
cd mol

Q.uAlCTnr
Plane augle Solid IUIIle Derlyed Ualta
Q,U.&.NTITY

Ul'II'r

SYMBOL

radiaD Iteradian

rad
It

UlfIT

8'1'1180£

n.rmJTIOK

Porce EnefIY Power Flus Flus deDiity Prequency Electric conductance Electromotive forc.

newton joule
watt

N

N =- 1 kl.m/sl

J
W Wb T

J-1N.m
I w- t J/s 1 Wb - 1 v., 1 T .. 1 Wb/ml I Hz - I cIs (a-I) I S-IA/V I V-IW/A I P. - I N/m l

Pr-.ur., Itrea

weber t.labuts ,iemea volt palCal

H.
S

V
P.